This invention relates to pipettes, and more particularly to pipettes having automatic mechanisms for identifying and/or removing tips.
Pipettes are commonly utilized to aspirate a fluid from one container or other source and to dispense the fluid to a second container or other receptacle. Since the fluid being aspirated and dispensed is frequently analyzed or otherwise tested after being dispensed, and in order for such testing or analysis to be accurate, it is important that a sample not be contaminated by fluid from a prior aspirated sample. While it is possible to wash a pipette tip between aspirations in order to reduce or eliminate such contamination, and for some pipette systems, particularly those utilizing fluid displacement, this is frequently done, washing the tips is expensive and time-consuming, and it is frequently difficult to remove all contaminants. Therefore, for many pipettes, particularly air displacement pipettes, it is cheaper and easier to replace the pipette tip after each use.
However, when a pipette tip is mounted to the nozzle, it is important that the tip be mounted with sufficient force to seal the nozzle so that fluid being aspirated and dispensed does not leak around the tip-nozzle junction, thereby preventing accurate quantities of fluid from being aspirated and dispensed, and the tip must be mounted with sufficient force to prevent the tip from falling off. However, if the tip is mounted with too much force, it can become difficult to remove the tip from the nozzle after use, resulting in significant strain on the operator""s hand. For this and other reasons, an operator working in a laboratory or other facility where large numbers of tips are replaced each day may experience repetitive stress injuries with current pipette designs as a result of repeated tip removals.
Heretofore, control on the force applied in mounting a tip to a nozzle has generally relied on the skill of the person doing the mounting. Thus, while for an illustrative embodiment, only two pounds of force may be required to properly mount a tip to the nozzle, operators may inadvertently be applying 10 to 15 pounds of force in mounting the nozzle, making nozzle removal far more difficult than necessary. However, without tactile guidance, an operator might overcompensate for this problem and not properly mount a nozzle. Further, while some tip removal mechanisms have existed for pipettes in the past, these have generally been manually operated and, since they have generally not controlled tip mounting force, they have frequently required that substantial force be applied by, for example, the operator""s thumb to successfully effect tip removal. This operation is therefore another potential cause of repetitive stress injuries. Alternatively, such tip removal schemes have been motor driven, increasing the size, cost and complexity of the pipette.
A related problem is that there are a variety of tips available for use with a given pipette and the pipette volume settings, particularly where these settings are automatically performed, need to be slightly adjusted for some tips to obtain the desired volumes of aspirated and/or dispensed fluid. The tips may for example have different length, volume, orifice diameter/size, shape and/or surface treatment (for example a low liquid retention coating). The tips may also be filtered or unfiltered, and if filtered, may have various special filtering elements, the presence and nature of filtering elements being a major factor in requiring volume adjustments for the pipette. While provision may be made for the user to input information on the tip being used either on the pipette or on a processor used therewith, this can be burdensome for the operator where a large number of pipetting operations are being performed. It also provides a source of pipetting error where the operator either forgets to identify a special tip used for a given operation or makes an erroneous entry, either because the operator doesn""t know the tip used or enters tip information incorrectly. It is also possible that the operator may select the wrong tip for a particular pipetting operation. It would therefore be preferable if the pipette could easily and quickly identify the tip being mounted as part of the tip mounting process without requiring any operator input, and could provide some type of feedback to the operator, for example when there is a change in tip used, to minimize inadvertent use of the wrong tip.
A need therefore exists for improved pipettes which overcome the various tip mounting, tip removal and tip identification problems identified above.
The tip mounting and removal problems indicated above are generally overcome in accordance with the teachings of this invention by storing part of the force used by the operator to mount the tip to a nozzle, actively limiting the force with which the tip is mounted to the nozzle, providing a sensory feedback to the operator when the tip is properly positioned on the nozzle and releasing the mechanical energy stored during the mounting of the tip in response to operator activation to facilitate the automatic removal of the tip. An overforce capability may be provided to supplement the stored energy for the removal of a stuck tip. Mechanisms used for the above may also be utilized in solving the tip identification problem.
More specifically, the invention provides a mechanism for facilitating the removal of a tip from a pipette nozzle which includes a spring loaded ejector sleeve through which the nozzle passes, the sleeve terminating near the end of the nozzle to which the tip is mounted when the sleeve is in a normal position, the sleeve being moved away from the end of the nozzle against the spring load when the tip is mounted to the nozzle. The sleeve includes a first latch portion which mates with a second latch portion of the pipette when the sleeve is in a retracted position to which it is moved when a tip is properly mounted to the nozzle to hold the sleeve in the retracted position against the spring load, a third latch portion being provided which is operable to unmate the first and second latch portions, freeing the sleeve to return in response to the spring load to its normal position. The sleeve engages the tip before reaching the normal position to facilitate removal of the tip. The tip removal mechanism may include an overforce mechanism operable to supplement the spring load in moving the sleeve to its normal position against a stuck tip to further facilitate removal of the tip. For one embodiment, the first latch portion is a keyhole slot formed in the sleeve, the second latch portion is a detent having a large portion which fits in an enlarged portion of the slot when the sleeve is in its retracted position and a small portion sized to fit in a narrow portion of the slot, the narrow portion being adjacent to the detent except when the sleeve is in the retracted position. For this embodiment, the third latch portion is a button operable for moving the small portion of the detent into the slot to unlatch the sleeve. For this embodiment, the detent may be spring-biased to move the large portion of the detent into the slot. For another embodiment, the first latch portion is a projection at a proximal end of the sleeve, the second latch portion is a mating lip on a latch plate biased to have the lip engage the projection when the sleeve is in its retracted position and the third latch portion is a portion of the latch plate which is manually operable to move the plate against its bias to move the lip away from the projection, permitting the sleeve to return to its normal position. For this embodiment, an angled surface on the plate may be provided which is positioned to engage an angled surface associated with the sleeve when the latch plate is moved beyond the point where the lip no longer engages the projection, the interaction of the two angled surfaces supplementing the spring load in moving the sleeve to its normal position against a stuck tip to further facilitate removal of the tip.
The tip removal mechanism preferably also includes a mechanism for controlling the force with which a tip is mounted to the nozzle. This mechanism for controlling may include mounting the nozzle to be movable away from a tip mounting force and against a bias spring. For this embodiment, the bias spring preferably has less load than the spring load applied to the ejector sleeve.
The ejector sleeve is preferably moved away from the tip receiving end of the nozzle by the tip. Alternatively, where tips are mounted in a rack having a protrusion adjacent each tip, the ejector sleeve may be moved away from the end of the nozzle by the protrusion adjacent the tip being mounted. For preferred embodiments, the mating of the first and second latch portions results in an operator perceptible feedback output, for example an audio, tactile or visual feedback output.
The invention also includes a mechanism for facilitating the removal of a pipette tip from a pipette nozzle which includes an ejector normally biased to a first position near an end of the nozzle to which the tip is mounted and movable as the tip is mounted to the nozzle against the bias, the ejector reaching a retracted position when the tip is fully mounted; and a latch for maintaining the ejector in the retracted position, the latch including a selectively operable latch release, the bias returning the ejector to its first position when the latch release is operated to facilitate ejection of the tip mounted to the nozzle. An overforce mechanism may be provided which is operable to supplement the bias in moving the ejector to its normal position against a stuck tip to further facilitate removal of the tip. A mechanism is preferably also provided for controlling the force with which the tip is mounted to the nozzle. There may also be a plurality of different tip types, each of which contacts both the ejector and the nozzle as it is mounted to the nozzle and moves against a bias force, each tip having a different base configuration which results in a difference in the relative displacement of the nozzle to the ejector. A mechanism can be provided for detecting such difference in relative displacement to identify tip type.
More generally, the invention includes a mechanism for facilitating the removal of a pipette tip from a pipette nozzle including a mechanism which stores mechanical energy when a tip is mounted to the nozzle and which releases the stored mechanical energy when the tip is to be removed to facilitate removal thereof. The mechanism for storing may include a latching mechanism operative when the mechanical energy is fully stored, with an operator detectable output being generated when the latching mechanism operates. A mechanism is preferably also provided which limits the force with which the tip is mounted to the nozzle and an overforce mechanism may also be provided for further facilitating removal of a stuck tip.
The invention may also include a mechanism for detecting the type of pipette tip being mounted to a pipette nozzle which includes a sleeve mechanism surrounding the nozzle, at least one of the sleeve mechanism and nozzle being mounted to be selectively retracted when in contact with a tip as a tip is pressed on the nozzle to be mounted thereto, each tip type having a different base configuration which results in a difference in the relative displacement of the nozzle to the sleeve mechanism, a mechanism being provided for detecting such difference in relative displacement to thus identify tip type. Where the sleeve has a selected stroke, the mechanism for detecting may include a sensor generating an output when the sleeve is retracted for its selected stroke and a detector for nozzle retraction, the detector output when the sensor generates an output being indicative of tip type.